Heat Pump and Method of Heating Fluid

ABSTRACT

A heat pump comprising an evaporator, a compressor and a heat exchanger is provided. The evaporator transfers heat from taken in air to a first fluid and expels the taken in air at a temperature cooler than ambient temperature. The compressor compresses and pumps the first fluid. The heat exchanger comprises a first passage for the heated compressed first fluid driven by the compressor and a second passage for a second fluid driven by thermal convection. A heat pump comprising a second heat exchanger that receives heated compressed first fluid from the compressor which heats compressed first fluid from the heat exchanger is also provided. Additionally, methods and systems for heating a fluid are also provided.

FIELD OF THE INVENTION

The present invention relates to a heat pump and method of heating afluid. In particular, but not exclusively, the present invention relatesto a thermosiphonic heat pump and thermosiphonic method of heating waterusing heat from the atmosphere.

BACKGROUND TO THE INVENTION

Hot water is costly to produce, a cost compounded by the high cost ofwater heaters. Electric, solar, gas and heat pump water heaters all havedisadvantages. Electric hot water systems are undesirable as they have acomparatively high cost of operation and generate considerablepollutants. Solar hot water heaters are expensive, heavily regulated inmany countries and they are unable to be used in some sites, such asboutique housing developments, for aesthetic reasons. Solar waterheaters usually require a booster energy source such as thenon-renewable energy sources of electricity and natural gas whichproduce pollutants.

Natural gas is another alternative to electric water heaters howeverthese systems also produce harmful greenhouse gases and use anon-renewable energy source.

Another method of providing hot water is heat pumps which extract heatfrom the surrounding atmosphere using a refrigerant gas and acompressor. Prior art heat pumps are expensive and rely on electricityto power a pump. Further the utility of prior art heat pumps is reducedas they are not capable of operating when the ambient temperature isbelow 10° C. which makes them unsuitable for many sites or increasestheir reliance on booster energy sources such as the above-mentionednon-renewable energy sources, electricity and natural gas.

Many of the water heaters in use in homes and other buildings areelectric, gas or solar powered, or a combination of these. Replacing allexisting hot water tanks would be an enormous cost and would take a longtime to gain a favourable energy and pollution cost/benefit ratio. Withthis in mind it is highly desirable that any alternative for providingless costly hot water has the capacity of fitting to existing watertanks.

In this specification, the terms “comprises”, “comprising” or similarterms are intended to mean a non-exclusive inclusion, such that anapparatus, method or system that comprises a list of elements does notinclude those elements solely, but may well include other elements notlisted.

OBJECT OF THE INVENTION

It is an object of the present invention to provide a heat pumpcomprising a thermosiphon which is a useful commercial alternative toexisting heat pumps. Further objects will be evident from the foregoingdescription.

SUMMARY OF THE INVENTION

In one form, although it need not be the only or indeed the broadestform, the invention resides in a heat pump comprising an evaporator thattransfers heat from taken in air to a first fluid and expels the takenin air at a temperature cooler than ambient temperature, a compressorfor compressing and pumping the first fluid and an improved heatexchanger, the improvement residing in the improved heat exchangercomprising a first passage for the heated compressed first fluid drivenby the compressor and a second passage for a second fluid driven bythermal convection.

The inventors' novel utilization of thermosiphon technology to drive thepassage of the second fluid eliminates the need for a pump to pump thesecond fluid which has the advantages of reducing cost, reducing energyusage and reducing both noise and green house gas pollution.

In one aspect the taken in air is heated above ambient temperature byheat generated by normal operation of the evaporator and heat istransferred from the heated taken in air to the first fluid.

In another aspect the heat pump also comprises a second heat exchangercomprising a third passage for heated compressed first fluid from thecompressor and a fourth passage for compressed first fluid from the heatexchanger that has exchanged heat with the second fluid.

In still another aspect the invention further includes a storage tankfilled with the second fluid.

Unlike prior art heat pumps the heat pump of the invention is capable ofoperating below 10° C. and even below 0° C.

In a second form the invention resides in a water heater comprising atank and a heat pump, the heat pump comprising an evaporator thattransfers heat from taken in air to a first fluid and expels the takenin air at a cooler temperature, a compressor for compressing and pumpingthe heated first fluid and an improved heat exchanger, the improvementresiding in the heat exchanger comprising a first passage for the heatedcompressed first fluid driven by the compressor and a second passage fora second fluid driven by thermal convection.

In another form, the invention resides in a method of heating waterincluding the steps of:

taking ambient air in through an evaporator;

heating a first fluid in the evaporator with the taken in air;

expelling the taken in air as relatively cool air;

compressing the heated first fluid;

pumping the heated compressed first fluid through a heat exchanger; and

heating water in the heat exchanger by exchanging heat from the heatedcompressed first fluid to the water whereby passage of the water isdriven by thermal convection.

Further features of the present invention will become apparent from thefollowing detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, preferred embodiments of the invention will bedescribed more fully hereinafter with reference to the accompanyingdrawings in which like reference numerals refer to like elements,wherein:

FIG. 1 shows a schematic diagram of a heat pump in accordance with anembodiment of the invention;

FIG. 2 shows a schematic diagram of a portion of a heat exchanger inaccordance with an embodiment of the invention;

FIG. 3 shows a cut away view of part of a heat exchanger in accordancewith an embodiment of the invention;

FIG. 4 shows one embodiment of the heat exchanger of the inventionillustrating the feature of different lengths and widths of the heatexchanger;

FIG. 5 shows a side by side arrangement for first and second passages inaccordance with an embodiment of the heat exchanger of the invention;

FIG. 6 shows a top and bottom arrangement for first and second passagesin accordance with an embodiment of the heat exchanger of the invention;

FIG. 7 shows another top and bottom arrangement for first and secondpassages in accordance with an embodiment of the heat exchanger of theinvention;

FIG. 8 shows a coaxial arrangement for first passage and second passageof a heat exchanger in accordance with an embodiment of the invention;

FIG. 9 shows a perspective view of an inner tube of the heat exchangerin accordance with one embodiment of the invention;

FIG. 10 shows a schematic diagram of a heat pump comprising an icemanagement system in accordance with an embodiment of the invention;

FIG. 11 shows a schematic diagram of a heat pump fitted to a tank inaccordance with an embodiment of the invention;

FIG. 12 shows a schematic diagram of a heat pump comprising an icemanagement system in accordance with another embodiment of theinvention;

FIG. 13 shows a schematic diagram of a heat pump comprising anelectrical element in accordance with another embodiment of theinvention; and

FIG. 14 shows a schematic diagram of a heat pump comprising an expansiondevice in accordance with another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is provided a heat pump 1 comprising anevaporator 2, a compressor 3 and a heat exchanger 4. As best seen inFIG. 2 the heat exchanger 4 comprises a first passage 5 and a secondpassage 6. A first fluid cycles through the first passage 5 and a secondfluid passes through the second passage 6. The heat exchanger 4 will bedescribed with reference to the first passage 5 being an outer tube 7and the second passage 6 being an inner tube 8, however the invention isnot limited to this embodiment.

FIG. 2 illustrates an embodiment of the improved heat exchanger 4wherein the outer tube 7 and the inner tube 8 are coaxial. In thiscoaxial embodiment the inner tube 8 is a core and the outer tube 7 is ajacket enclosing the coaxial core.

The evaporator 2 as best seen in FIG. 3 comprises an air intake 9 and anair exhaust 10. The embodiment depicted in FIG. 3 shows the air intake 9additionally comprising a fan 11 which assists in the circulation of airthrough the heat pump 1, however the fan 11 is not an essential elementof the evaporator 2. Air is drawn into the evaporator 2 through the airintake 9. The taken in air is at ambient temperature and is used to heatthe first fluid located inside the evaporator 2. The heated first fluidis then pumped, by the compressor 3, from evaporator 2 to the compressor3. The air that was taken into the evaporator 2 as ambient air havingexchanged its heat with the first fluid is expelled from the evaporator2 as relatively cooler air.

Advantageously, in one embodiment, like that shown in FIG. 3, theevaporator 2 is configured so the air drawn into the evaporator 2 whichis at ambient temperature passes over or through one or more area of theevaporator 2 that becomes heated during normal operation of theevaporator 2. In this manner the drawn in ambient air becomes heated toa temperature above ambient temperature. This heating of the ambient airby operational heat occurs at no additional energy cost and furtherincreases the efficiency and operable temperature range of the heat pump1 over and above that of prior art heat pumps. The heated ambient air isused in the same manner as ambient air to heat the first fluid in thefirst passage 5.

The compressor 3 compresses the heated first fluid which has the effectof further heating the first fluid. The heated compressed first fluid isthen pumped, by compressor 3, from the compressor 3 to the heatexchanger 4.

It is understood that the first fluid may be gas or liquid and phasedepends on pressure and temperature. Therefore the phase of the firstfluid is dependent on the temperature and pressure at each point in theheat pump 1. However, for ease of description, from exiting thecompressor 3 until entering the evaporator 2 the first fluid will bereferred to as “compressed first fluid” and from exiting the evaporator2, where it is decompressed, until entry into the compressor 3 the firstfluid will be referred to as “first fluid”. In a preferred embodimentthe first fluid is a refrigerant.

The coaxial arrangement of the outer tube 7 and the inner tube 8depicted in FIG. 2 allows efficient heat exchange between the firstfluid and the second fluid. The hollow construction of the outer tube 7allows the first fluid to pass therethrough, as driven by compressor 3.The inner tube 8 is also of hollow construction and forms a convectionpath that allows the passage of the second fluid through the secondpassage 6 to be driven by thermal convection. The motion of the secondfluid by thermal convection is termed thermosiphoning and is aconsequence of the heat exchange between the heated compressed firstfluid entering the outer tube 7 and the second fluid passaging throughthe inner tube 8.

The heated compressed first fluid entering the outer tube 7 exchangesheat with the second fluid and exits the outer tube 7 as cool compressedfirst fluid. The second fluid enters the inner tube 8 as relatively coolsecond fluid and exits the inner tube 8 as heated second fluid.

The cool compressed first fluid is pumped out of the outer tube 7 andreturns to the evaporator 2 where it is decompressed. Afterdecompression the cool first fluid is again heated in the evaporator 2by taken in air and the above-described heat-exchange process continuesin a cycle with the cycling of the first fluid driven by the compressor3 and the passage of the second fluid driven by convection.

Like the taken in air, any vapour produced during decompression of theheated relatively cool first fluid is expelled through the air exhaust10.

The heat pump 1 of the invention functions to heat a pump-driven firstfluid, for example a refrigerant, through extracting heat from ambientair and in turn heating a thermosiphon-driven second fluid, for examplewater, by exchanging heat from the first fluid to the second fluid. Inone form the heat pump 1 is a refrigerant heating system. The pumpingforce required to pump the first fluid through the heat pump 1 isprovided by the compressor 3. However, beneficially in one embodimentthe heat pump 1 can also comprise a pump, not shown, to provideadditional pumping force.

The coaxial arrangement of the first passage 5 and second passage 6described above and illustrated in FIG. 2 is a particularly efficientarrangement for heat exchange from the first fluid to the second fluid.FIG. 4 illustrates another feature of the coaxial embodiment of the heatexchanger 4 wherein the inner tube length 12 is located entirely withinthe outer tube 7, while the inner tube inlet 13 and the inner tubeoutlet 14 are located external to the outer tube 7.

The above refrigerant heating cycle has been described with reference tothe first fluid being pumped through the first passage 5 of the heatexchanger 4 and the second fluid passing through the second passage 6 ofthe heat exchanger 4 driven by a thermosiphon. It is understood that thepassage of the first and second fluids could be swapped, with the firstfluid being pumped through the second passage 6 of the heat exchanger 4and the second fluid passing through the first passage 5 of the heatexchanger 4 driven by thermal convection. In this alternateconfiguration the flow of the first fluid and second fluids must bedesigned with regard to the second fluid rising when heated as driven bythermal convection. Likewise, the alternate coaxial arrangement whereinthe first passage 5 of the heat exchanger 4 is the inner tube 8 and thesecond passage 6 of the heat exchanger 4 is an outer tube 7 is alsoencompassed in coaxial embodiments of the heat exchanger 4.

The coaxial arrangement of the outer tube 7 and the inner tube 8depicted in FIG. 2 allows efficient heat exchange between the firstfluid and the second fluid. It is not a requirement that the firstpassage 5 and the second passage 6 be arranged coaxially, anyarrangement of the first passage 5 and second passage 6 allowing heattransfer from the first fluid to the second fluid and thermal convectionof the second fluid (thermosiphoning) is encompassed. Illustrativefurther examples of adjacent or proximal first passage 5 and secondpassage 6 arrangements are shown in FIGS. 5-8.

FIG. 5 shows a side-by-side embodiment of the heat exchanger 4 in whichthe first passage 5 comprises a left hand side tube 15 and the secondpassage 6 comprises a right hand side tube 16. FIG. 6 shows another heatexchanger 4 embodiment in which the first passage 5 comprises a top tube18 and the second passage 6 comprises a bottom tube 19. FIG. 7 shows asimilar top and bottom heat exchanger 4 arrangement in which the firstpassage 5 comprises a top tube 21 and the second passage 6 comprises abottom tube 22. The embodiments depicted in FIG. 6 and FIG. 7 differ inthat FIG. 6 illustrates a top and bottom arrangement at an angle greaterthan 900 with respect to vertical and FIG. 7 illustrates a top andbottom arrangement at an angle less than 900 with respect to vertical.

Another suitable arrangement is depicted in FIG. 8 wherein the firstpassage 5 and second passage 6 are coaxial and the outer first passagecomprises an encircling outer tube 24 forming a series of concentricrings wound around the second passage which comprises an inner core tube25.

To further increase the efficiency of heat exchange in some embodimentsthe surface(s) across which heat exchange takes place are in directcontact. Such an embodiment is shown in FIG. 8 wherein the surface ofthe encircling outer tube 24 is in direct contact with the surface ofthe inner core tube 25.

To still further increase the efficiency of heat exchange the firstpassage 5 and second passage 6 in some embodiments share a wall, asdepicted in FIGS. 2 and 5-7. FIG. 2 shows a common wall 26 which formsthe inner surface of the outer tube 7 and the outer surface of the innertube 8. Similarly, common wall 17, common wall 20 and common wall 23 aredepicted in FIGS. 5, 6 and 7 respectively. The common walls 26, 17, 20and 23 are walls across which heat exchange from the first fluid to thesecond fluid occurs. In the shared wall embodiment the first fluid andthe second fluid pass across opposing surfaces of the common wall 26,17, 20, 23. Advantageously, the efficient heat exchange of the commonwall embodiment can also be achieved in the side-by-side arrangement asshown in FIG. 5 and in the top-and-bottom arrangement as shown in FIGS.6 and 7.

To still further increase the efficiency of heat exchange the firstpassage 5 and second passage 6 of the heat exchanger 4 are constructedin one-piece and the surfaces of the first passage 5 and the secondpassage 6 across which heat exchange occurs are constructed in a shapethat increases the surface area of the surface(s) across which heatexchange takes place. Suitable shapes for increasing the surface area ofthe first passage 5 and the second passage 6 are the ribbed shape 27depicted in FIG. 2 and the raised spiral shape 28 depicted in FIG. 9.

For efficient thermosiphoning the second passage 6 is positioned so thatthe second passage 6 runs vertically, or close to vertical. Such avertical embodiment is shown in FIG. 5. In other embodiments the secondpassage 6 is positioned within ±45° from vertical. Embodiments whereinthe second passage lies at an angle vertical ±45° from vertical areshown in FIGS. 6 and 7.

In preferable embodiments to increase the heat exchange between thefirst fluid and the second fluid the fluids flow in opposite directions,i.e. the flows of the first and second fluid are counter-current. Inthis counter-current embodiment the second passage 6 must be positionedin an orientation that allows the second fluid to be driven by thermalconvection alone.

A disadvantage of prior art heat pumps is that they cannot operateeffectively below 10° C. where the heat pump evaporator develops ice.The conventional solution to eliminate ice, like that adopted in airconditioners, is to commence a reverse cycle. This however isundesirable in water heating as it would cool the water and inembodiments where the heat pump is fitted to a tank, such as describedbelow, would cycle cold water into the water storage tank.

FIG. 10 shows heat pump 101, which incorporates an ice management system129, that makes operation below 10° C. possible.

The ice management system 129 comprises a second heat exchanger 130which comprises a third passage 131 through which heated compressedfirst fluid that has exited the compressor 103 passes as driven by thepumping action of the compressor 103. The second heat exchanger 130 alsocomprises a fourth passage 132 through which cool compressed first fluidthat has exited the heat exchanger 104 passes and is also pumped bycompressor 103.

In the second heat exchanger 130 the heated compressed first fluidexchanges heat with the cool compressed first fluid. Therefore the firstfluid exiting the third passage 131 is relatively cool heated compressedfirst fluid and the first fluid exiting the fourth passage 132 isrelatively warm cool compressed first fluid. It is to be understood thatthe relatively cool heated compressed first fluid is not cool per se andis only relatively cool compared to the heated compressed first fluid.The relatively cool heated compressed first fluid can function in theheat exchanger 104 to exchange heat with the second fluid to produceheated second fluid.

The heating in the third passage 131 of the cool compressed first fluidto relatively warm cool compressed first fluid reduces the incidence ofice production and has the significant effect of allowing the heat pump101 to operate effectively at temperatures as low as 0° C. to 4° C.

In another embodiment the ice management system 129 further comprises aconstant pressure/temperature valve (not shown) that detects thetemperature of the first fluid at entry to the evaporator 102. Theconstant pressure/temperature valve functions to operate the icemanagement system 129 when the temperature of the circulating firstfluid entering the evaporator 102 falls below a setpressure/temperature. In one embodiment the constantpressure/temperature valve functions to operate the ice managementsystem 129 when the compressed first fluid entering the evaporator 102is at a pressure between about 300-25000 kpa. In another embodiment theconstant pressure/temperature valve functions to operate the icemanagement system 129 when the compressed first fluid entering theevaporator 102 is at a temperature less than 10° C., or at a temperaturebetween about 0 and 10° C.

The efficiency and the low temperature operability of the heat pump 1,101, and heat pumps described below can be further increased byutilizing a low boiling point refrigerant as the first fluid. Prior artheat pumps use air conditioning refrigerant as the first fluid givinghot water at about 55° C. The heat pump 1, 101 and heat pumps describedbelow, are designed to use either conventional refrigerants, such as airconditioning refrigerants, or to use a lower boiling point refrigerant.Utilization of a lower boiling point refrigerant produces highercondensing temperatures and generates the benefit of hotter water.

The heat pump 1 has an expected average coefficient of performance (COP)at 55° C. of 3 to 3.2 which is equivalent to other domestic hot waterheat pumps. At 65° C. the expected COP of the heat pump 1 is about 2.

A further important advance made by the present inventors is thecircumvention of superheating of the first fluid which occurs in priorart heat pumps. Prior art heat pumps when fitted to a water tank returnthe first fluid from the heat exchanger to the compressor directlyadjacent to the hottest second fluid which sends the first fluid to theevaporator hotter than is desirable and is inefficient. The inventorsprevent superheating of the first fluid by advantageously locating theheat pump 1, 101 and the heat pumps described below, external to thetank and by insulating the path of the first fluid. FIG. 11 depicts anembodiment of the heat pump 1 located external to the tank 34.

A feature of the heat pump 1, 101 and the heat pumps described below ofgreat benefit is that they are suitable for easy retrofit installationon existing water storage tanks, such as domestic water tanks andincluding domestic water tanks with a capacity of, for example, 80, 125,160, 180, and 250 litres or greater. The heat pump 1, 101 and thosedescribed below are easily retrofitted, via for example T-pieces, towater tanks with a separate flow outlet and return inlets. Additionally,the heat pump 1, 101 and those described below are suitable forinstallation onto existing water tanks that do not comprise a separateflow outlet and return inlet.

When used in conjunction with a tank the heat pump 1, 101 and thosedescribed below, will draw the second fluid, for example water, from thetank. As shown in FIG. 11 the tank 34 comprises a tank inlet 35 and atank outlet 36. The tank inlet 35 and the tank outlet 36 are connectedto the second passage 6 of the heat exchanger 4. The second fluid, forexample water, stored in the tank 34 exits the tank 34 through the tankoutlet 36, enters the second passage 6 of the heat exchanger 4 where itis heated and is returned to the tank 34 as heated second fluid throughthe tank inlet 35. As described above, when the second fluid passesthrough the second passage 6 it is heated by heated compressed firstfluid cycling through the first passage 5 of the heat exchanger 4 andthe passage of the second fluid is driven by convection. Therefore thesecond fluid that returns to the tank 34 has been heated by heat fromthe first fluid.

The circular heating motion of the second fluid from the tank 34 throughthe heat exchanger 4 and back to the tank 34 is driven by thermalconvection so that the greater the difference in temperature between thewater in the heat exchanger 4 and the water in the storage tank 34, thefaster the flow between them.

As shown in FIG. 11, to maximise efficiency of the thermosiphon the tank34 preferably has the tank outlet 36 located at the bottom of the tank34 and the tank inlet 35 located at the top of tank 34. In thisarrangement the heat exchanger 4 can be conveniently mounted onto theside of the tank 34 with the second passage 6 positioned vertically, orclose to vertically, i.e. within ±45° of vertical.

FIG. 12 shows another embodiment of a heat pump 201 that comprises anice management system 229. As with the heat pumps 1, 101 describedabove, the passage of the first fluid in heat pump 201 is cyclical. Thecycle of the first fluid in heat pump 201 is described below.

After exchanging heat with the second fluid in heat exchanger 204, thefirst fluid is cooled in a cooling loop 240 of evaporator 202. Toefficiently cool the second fluid the cooling loop 240 may be positionedso that the relatively cooler air that has exchanged its heat with thefirst fluid flows over it. This cooling of the first gas draws heat outof heat pump 201 and increases the efficiency of the heating of thefirst fluid in the evaporator 202.

After exiting the evaporator 202 the first fluid passes through icemanagement system 229, which functions similarly to ice managementsystem 29 and can also be turned on and off with fluctuations in ambienttemperature. When ice management system 229 is functioning the firstfluid that has exited the evaporator 202 will be heated in the icemanagement system 229 by the first fluid that has exited compressor 203.

The first fluid exits the ice management system 229, is heated inheating loop 242 of evaporator 202 by taken in ambient air and is thenpumped through compressor 203.

Next if the ice management system is operating hot gas bypass valve 245will direct a portion of the heated compressed first fluid through theice management system 229 to mix with and heat the first fluid that hasexited the cooling loop 240. The heated mixed first fluid then proceedsinto the heating loop 242. A person of skill in the art is readily ableto select an appropriate portion of the heated compressed first fluid todirect through the ice management system 229. The portion may be, forexample, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%,15%, 16%, 17%, 18%, 19%, 20%, 30%, 40% or 50% In one embodiment theportion is up to 20% is used.

The heated compressed first fluid that is not directed by the valve 245to the ice management system 229 passes through the heat exchanger 204where it heats the second fluid from tank 234.

The cooling loop 240 and heating loop 242 are shown to comprise two andfour longitudinal segments respectively. A person of skill in the art isreadily able to choose an appropriate number of longitudinal and lateralsegments.

The ice management system 329 shown in FIG. 13 comprises a low wattageelectrical element 350 that is switched on and heats up when the ambientair temperature is ≦5° C. The switching on and off of the electricalelement 350 may be controlled electronically and automatically using atemperature sensor to detect the ambient air temperature. The heating ofthe electrical element 350 heats the first fluid in the ice managementsystem 329.

In one embodiment the presence of electrical element 350 allows theelimination of bypass valve 245.

At temperatures ≦5° C. the speed of the fan (not shown) in theevaporator 302 may also be increased.

The heat pump 201 shown in FIG. 14 comprises an expansion device 460which operates to reduce the pressure of the first fluid which therebycools the first fluid. This cooling of the first gas draws heat out theheat pump 401 and increases the efficiency of the heating of the firstfluid in the evaporator 442. In one embodiment the expansion device 460is a Tx valve and in another embodiment is a capillary tube.

The inventors have shown that heat pump 201 operates effectively at −1°C.

Other tests by the inventors have also shown that an electrical element350 drawing only 300 watts operates effectively in heat pump 301. Thiscompares favourably with prior art heat pumps which require 3 000-3 600watts to operate.

The invention also encompasses a method of heating water using the heatpump 1, 101, 201 described above to heat water.

In addition to encompassing a method of heating water the inventionencompasses a system for heating water comprising a means for taking inambient air, heating a first fluid with the taken in air and expellingthe taken in air as relatively cooler air, a means for compressing theheated first fluid and for pumping the heated compressed first fluidthrough a heat exchanger, and an improved means for heating waterwherein the improvement resides in the water being propelled through theimproved heat exchanger by thermal convection and the water is heated bythe heated compressed first fluid.

Hence, the heat pump 1, 101, 201, method and system of using the heatpump 1, 101, 201 provide a solution to the problems of reducing relianceon non-renewable energy resources, reducing pollution and providing lowcost hot water by virtue of the inventors novel utilization of thenatural thermal convection of thermosiphon technology to passage fluidssuch as water.

Further, the heat pump 1, 101, 201 and method and system of theinvention are operable at lower temperatures than prior art heat pumpswhich extends the use of heat pumps into hitherto unworkable locations.

The retrofittable aspect of the invention has the further advantages ofreducing cost of replacement as storage tanks are not required to bereplaced and space is saved as the heat pump 1, 101, 201 of theinvention can be mounted on existing tanks.

Throughout the specification the aim has been to describe the inventionwithout limiting the invention to any one embodiment or specificcollection of features. Persons skilled in the relevant art may realizevariations from the specific embodiments that will nonetheless fallwithin the scope of the invention.

1. A heat pump comprising an evaporator that transfers heat from takenin air to a first fluid and expels the taken in air that has exchangedheat at a temperature cooler than ambient temperature, a compressor forcompressing and pumping the first fluid and an improved heat exchanger,the improvement residing in the improved heat exchanger comprising afirst passage for the heated compressed first fluid driven by thecompressor and a second passage for a second fluid driven by thermalconvection.
 2. The heat pump according to claim 1 wherein the taken inair is heated above ambient temperature by heat generated by normaloperation of the evaporator and heat is transferred from the heatedtaken in air to the first fluid.
 3. The heat pump according to claim 1wherein the first passage and second passage are coaxial.
 4. The heatpump according to claim 1 wherein the first passage and second passageare side by side.
 5. The heat pump according to claim 1 wherein thefirst passage and second passage share a common wall.
 6. The heat pumpaccording to claim 5 wherein the common wall is ribbed.
 7. The heat pumpaccording to claim 5 wherein the common wall comprises a raised spiral.8. The heat pump according to claim 1 wherein the evaporator furthercomprises a cooling loop.
 9. The heat pump according to claim 8 whereinthe cooling loop is positioned to be exposed to the air that hasexchanged heat.
 10. The heat pump according to claim 1 furthercomprising a second heat exchanger that receives heated compressed firstfluid from the compressor and compressed first fluid from the heatexchanger.
 11. The heat pump according to claim 10 wherein a valvecontrols flow of the first fluid from the compressor to the second heatexchanger.
 12. The heat pump according to claim 10 wherein the secondheat exchanger further comprises a third passage for heated compressedfirst fluid from the compressor and a fourth passage for compressedfirst fluid from the heat exchanger that has exchanged heat with thesecond fluid.
 13. The heat pump according to claim 10 wherein the heatedcompressed first fluid from the compressor and the compressed firstfluid from the heat exchanger mix in the second heat exchanger.
 14. Theheat pump according to claim 10 wherein the second heat exchangerfurther comprises an electrical element.
 15. The heat pump according toclaim 10 wherein a valve is positioned between the first heat exchangerand the evaporator to allow pressure of the first fluid to be reduced.16. The heat pump according to claim 15 wherein the valve is a Tx valve.17. The heat pump according to claim 10 wherein a capillary tube ispositioned between the first heat exchanger and the evaporator to allowpressure of the first fluid to be reduce.
 18. The heat pump according toclaim 1 further comprising a storage tank filled with the second fluid.19. A water heater comprising a tank and a heat pump, the heat pumpcomprising an evaporator that transfers heat from taken in air to afirst fluid and expels the taken in air that has exchanged heat at acooler temperature, a compressor for compressing and pumping the heatedfirst fluid and an improved heat exchanger, the improvement residing inthe heat exchanger comprising a first passage for the heated compressedfirst fluid driven by the compressor and a second passage for a secondfluid driven by thermal convection.
 20. A method of heating waterincluding the steps of: taking ambient air in through an evaporator;heating a first fluid in the evaporator with the taken in air; expellingthe taken in air as relatively cool air; compressing the heated firstfluid; pumping the heated compressed first fluid through a heatexchanger; and heating the water in the heat exchanger by exchangingheat from the heated compressed first fluid to the water whereby passageof the water is driven by thermal convection.
 21. The method of claim 20further including the step of heating the first fluid with the heatedcompressed first fluid.
 22. The method of claim 21 further comprisingreducing the pressure of the first fluid.
 23. A system for heating watercomprising: a means for taking in ambient air, heating a first fluidwith the taken in air and expelling the taken in air as relativelycooler air; a means for compressing the heated first fluid and forpumping the heated compressed first fluid through a heat exchanger; anda means for heating water; wherein the water is heated by the heatedcompressed first fluid and the water is propelled by thermal convection.24. The system of claim 23 further comprising a means for heating thefirst fluid with the heated compressed first fluid.
 25. The system ofclaim 23 further comprising a means for reducing the pressure of thefirst fluid.